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AMD-K6

Processor

AMD-K6
Processor
Thermal Solution Design
Application Note
Publication # 21085 Rev: I Issue Date: February 1999 Amendment / 0
Trademarks AMD, the AMD logo, K6, and combinations thereof are trademarks, and AMD-K6 is a registered trademark of Advanced Micro Devices, Inc. Other product names used in this publication are for identification purposes only and may be trademarks of their respective companies.
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AMD-K6® Processor Thermal Solution Design
Contents
AMD-K6® Processor Thermal Solution Design
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Contents
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AMD-K6® Processor Thermal Solution Design
List of Figures
Figure 1. Passive Heatsink Thermal Model . . . . . . . . . . . . . . . . . . . . 4 Figure 2. Processor Heat Dissipation Path . . . . . . . . . . . . . . . . . . . . 4 Figure 3. CPGA Package Thermal Resistance Model. . . . . . . . . . . . 5 Figure 4. Voltage Regulator Placement . . . . . . . . . . . . . . . . . . . . . . . 7 Figure 5. Airflow for a Heatsink with Fan . . . . . . . . . . . . . . . . . . . . . 8 Figure 6. Airflow Path in a Dual-Fan System . . . . . . . . . . . . . . . . . . 8 Figure 7. Airflow Path in an ATX Form-Factor System . . . . . . . . . . 9 Figure 8. Standard Mid-Tower Case . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 9. Measuring Case Temperature. . . . . . . . . . . . . . . . . . . . . . 12
List of Tables
Table 1. Table 2. AMD-K6 Processor Family TCASE Specifications . . . . . . . 1 Summary of Chassis Box Fan Configurations . . . . . . . . . 10
List of Figures and Tables
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List of Figures and Tables
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AMD-K6® Processor Thermal Solution Design
Revision History
Date March 1998 March 1998 March 1998 March 1998 May 1998 May 1998 May 1998 Aug 1998 Aug 1998 Aug 1998 Nov 1998 Nov 1998 Rev E E E E F F F G G G H H Description Improved detail of Figure 1, "Passive Heatsink Thermal Model, " on page 4 and Figure 4, "Voltage Regulator Placement, " on page 7. Added system design considerations for fansink implementations. See "Heatsink and Fan" on page 7. Combined recommended fansink solutions into one table. See Table 2, "AMD-K6® Processor Model 6 Fansink Recommendations." Added new fansink manufacturers and models to Table 4, "Manufacturer Contact List." Revised "Recommended Fansinks for the AMD-K6® Processor Model 7 and AMD-K6®-2 Processor Model 8" to include AMD-K6-2 processor Model 8 information. Revised Table 2, "AMD-K6® Processor Model 6 Fansink Recommendations" and Table 4, "Manufacturer Contact List." Added Table 3, "Additional AMD-K6® Processor Models 7 and AMD-K6®-2 Processor Model 8 Fansink Recommendations." Removed package thermal specifications tables. For thermal specifications, added reference to the applicable AMD-K6 and AMD-K6-2 Processor Data Sheets. Revised Table 2, "AMD-K6® Processor Model 6 Fansink Recommendations" and Table 4, "Manufacturer Contact List." Added recommended 350 MHz AMD-K6-2 processor thermal solutions to Table 3, "Additional AMD-K6® Processor Model 7 and AMD-K6®-2 Processor Model 8 Fansink Recommendations." Revised Figure 9, "Measuring Case Temperature, " on page 12. Combined paragraphs "Recommended Fansinks for the AMD-K6® Processor Model 6" and "Recommended Fansinks for the AMD-K6® Processor Model 7 and AMD-K6®-2 Processor Model 8" into one paragraph. Replaced Recommended Fansinks (Tables 2 and 3) and the Manufacturer Contact List (Table 4) with a reference to the Recommended Thermal Solution section of the AMD website. Added references for the AMD-K6-III processor, where applicable. Added Table 1, "AMD-K6® Processor Family TCASE Specifications." Revised "Thermal Power Utility" on page 12 to reflect the latest recommended utility.
Nov 1998 Feb 1999 Feb 1999 Feb 1999
Revision History
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Revision History
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AMD-K6® Processor Thermal Solution Design
Application Note
AMD-K6
Processor Thermal Solution Design
Unless otherwise noted, the information in this application note pertains to all processors in the AMD-K6® family, which includes the AMD-K6 processor (Models 6 and 7), the AMD-K6-2 processor (Model 8), and the AMD-K6-III processor (Model 9).
Introduction
The operating specification for the AMD-K6 processor family calls for the case temperature (TCASE) to be in the range of 0°C to TCASE Max. It is important to maintain the case temperature w i t h i n t h e s p e c i f ic a t i o n fo r n o rm a l o p e ra t io n . I f t h e specification is exceeded, the result can be functional failures, damage to the device, or reduction in long term reliability. Table 1 on page 1, lists the TCASE specifications for the desktop AMD-K6 processor family. Table 1.
AMD-K6® AMD-K6-2 AMD-K6-III
Note:
AMD-K6® Processor Family TCASE Specifications
Minimum 0°C 0°C 0°C Maximum 70°C 60°C, 65°C, or 70°C 65°C Note
Processor Family
Refer to the AMD-K6®-2 Processor Data Sheet, order# 21850 for operating specifications as they apply to each AMD-K6-2 offering.
Introduction
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An effective thermal management system is the best way to maintain the case temperature within specification. In addition to the thermal characteristics and power dissipation of the processor, the temperature of the processor case is dependent on internal ambient temperature and air velocity. The internal ambient temperature is affected by several variables - electronic components, peripherals, thermal characteristics of the chassis, and external ambient temperature. Thermal management consists of heatsinks, thermal interface materials, heatsink clips, fans, chassis ventilation, and component placement. This application note is intended to guide the system designer through the process of developing an effective thermal solution for the AMD-K6 processor. For information about the thermal specifications for the following AMD-K6 processors:
AMD-K6 processor Model 6 (0.35-µm process technology) and the AMD-K6 processor Model 7 (0.25-µm process technology), refer to the AMD-K6® Processor Data Sheet, order# 20695. AMD-K6-2 processor Model 8 (0.25-µm process technology), refer to the AMD-K6®-2 Processor Data Sheet, order# 21850. AMD-K6-III processor Model 9 (0.25-µm process technology), refer to the AMD-K6®-III Processor Data Sheet, order# 21918.
System Conditions
The environmental specifications on most systems guarantee o p era t io n fo r ex t e rna l a m b ie n t s u p t o 35 ° C. M o st P C chassis / system boxes result in an internal 10°C increase in temperature over the external ambient temperature. In general, this means the thermal solution should be designed to allow an internal ambient (TA) of 45°C.
Introduction
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AMD-K6® Processor Thermal Solution Design
Thermal Solutions
Heatsink
Figure 1 on page 4 shows the thermal model of a processor with a passive thermal solution. The thermal resistance of a heatsink is determined by the heat dissipation surface area, the material and shape of the heatsink, and the airflow volume through the heatsink. In general, the larger the surface area the lower the thermal resistance. Heatsink designs use fins to increase the amount of dissipating surface area in contact with the ambient air. A larger surface area usually results in a lower thermal resistance. Some designs implement cross-cutting along the fins to allow omnidirectional airflow through the heatsink. The required thermal resistance of a heatsink ( SA ) can be calculated using the following example: If:
Using an interface material with a low thermal resistance of approximately 0.20 ° C / W (i.e. thermal grease), the required thermal resistance of the heatsink (SA) is calculated as follows:
Where:
Thermal Solutions
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Ambient Air
Temperature Delta (Case-to-Ambient) Thermal Resistance (°C / W)
Sink Case
Figure 1. Passive Heatsink Thermal Model
Heat Dissipation Path
Figure 2 illustrates the heat dissipation path of the processor. Due to the lower thermal resistance between the processor die junction and case, most of the heat generated by the processor is transferred from the top surface of the case. The small amount of heat transferred from the bottom side of the processor can be safely ignored due to high thermal resistance (the processor socket blocks convection).
Ambient Temperature
Thin Lid Case Temperature
Figure 2. Processor Heat Dissipation Path Figure 3 on page 5 illustrates the overall thermal resistance model of a socketed AMD-K6 processor with a heatsink att ached. The t herma l resistance of t he primary heat dissipation path is much lower than the secondary heat dissipation path. Therefore, most of the heat is transferred from the top side of the processor. In Figure 3, CA represents the thermal resistance from the top of the case to ambient. It includes the thermal resistance of the thermal interface material and the heatsink, which must be considered when designing a thermal solution for the AMD-K6 processor. 4 Thermal Solutions
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Thin Lid Ceramic substrate Heat Sink Clip Print-Circuit Board
Heat Sink Thermal Interface Material Die ZIF Socket
Primary Heat Dissipation Path
Radiation Convection
Ambient
External Resistance
Heat Sink Thermal Interface Material Thin Lid and Grease Silicon
Case Temperature
Chip Junction
Junction Temperature
Underfill
PGA Package
C4 Bumps Ceramic Substrate Package Pins Print-Circuit Board and Socket
External Resistance
Radiation Convection
Secondary Heat Dissipation Path
Figure 3. CPGA Package Thermal Resistance Model
Interface Materials
The interface material used between the heatsink and processor is important. The purpose of this material is to fill any microscopic air gaps and ensure a thermally efficient path is established for heat to flow from the package into the heatsink. There are several different types of thermally conductive interface material in use today. The most common are grease, wax, thermal pads / tapes, and epoxy. While dry interfaces (pads and tapes) are often the easiest to use, they have the poorest thermal resistance. They are not recommended because small pockets of air can be trapped during installation. Wet or paste interfaces (grease, gel, wax, and epoxy) have lower thermal resistances and allow air bubbles to migrate out of the interface material. Although epoxy, when handled correctly, can provide a reasonable thermal interface, it is not a reliable mechanical attachment. Caution should also be taken with pre-applied waxes, because pockets of air (a poor thermal conductor) can be Thermal Solutions 5
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trap p e d b en eath the heats i nk d ur i ng as s embly. AM D recommends the use of grease and gels as thermal interfaces. These materials are able to maintain the lowest thermal resistance more consistently. In general, these materials can achieve a thermal resistance of 0.15 to 0.3°C / W. The application of interface material, in addition to material type, is also important. Its purpose is simply to fill microscopic air gaps and ensure a thermally efficient path for heat transfer. Only a thin layer of interface material is desired between the heatsink and processor. Excessive amounts of interface material will restrict the flow of heat to the heatsink and thereby make the thermal solution less effective. Due to the light weight of most heatsinks, mechanical clips are the recommended method of attachment. In addition to providing stability, clips provide approximately 10-15 pounds of downward pressure on the heatsink to minimize the thermal resistance of the thermal interface material.
Layout and Airflow Considerations
Voltage Regulator
Voltage regulators, typically power transistors, are used to provide the core and I / O voltages to the processor. In most designs, separate heatsinks are also required to dissipate the heat from the power transistors. The processor heatsink fins should be aligned parallel to the chassis airflow and the voltage regulators as shown in Figure 4 on page 7. With this alignment, the heat generated by the voltage regulators has minimal effect on the processor.
Layout and Airflow Considerations
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Voltage Regulator (VCC Core)
Heatsink Fins Aligned With Airflow
Airflow
Voltage Regulator (VCC I / O)
Figure 4. Voltage Regulator Placement
Heatsink and Fan
A heatsink and fan combination, or fansink, can deliver even better thermal performance than a heatsink alone. More importantly, airflow requirements in a system design are not as critical with a fansink. The fan pulls air from above the fan, through the heatsink, and out the heatsink sides. When using a fansink solution, the best location for the voltage regulators is on the side of the processor, in the path of the air exiting the fansink (See Figure 5 on page 8). Such a location guarantees that the heatsinks on both the processor and the regulator receive adequate airflow. Fansinks are more effective when the following design techniques are employed:
To avoid impeding airflow within the chassis to the fansink, route ribbon cables between the system motherboard and chassis drive bays. To provide a sufficient volume of air to the fansink, maintain a 1 / 2 inch clearance above the fansink.
Layout and Airflow Considerations
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Airflow
Ideal areas for voltage regulator
Figure 5. Airflow for a Heatsink with Fan
Airflow Management in a System Design
Complete airflow management in a system is important. In addition to the speed and volume of air, the path of the air is also important. Figure 6 shows the airflow in a dual-fan system. The fan in the front end pulls cool air into the system through intake slots in the chassis. The power supply fan acts as an exhaust and forces the hot air out of the chassis. The thermal performance of the heatsink can be maximized if it is located in the shaded area with the fins oriented parallel to the airflow path.
Fan Main Board P / S
V e n t s Fan Vents Front
Drive Bays
Figure 6. Airflow Path in a Dual-Fan System 8 Layout and Airflow Considerations
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AMD-K6® Processor Thermal Solution Design
Airflow Management in the ATX Form Factor
Figure 7 shows the airflow management in a system using the ATX form-factor. The orientation of the power supply fan and the motherboard are modified in the ATX platform design. The power supply fan generates airflow through the chassis and across the processor. The processor is located near the power supply fan where it can receive maximum airflow without an auxiliary fan. This arrangement significantly improves the airflow across the processor with minimum installation cost.
Air Vents
Drive
Figure 7. Airflow Path in an ATX Form-Factor System
Additional Box Fans
Additional box fans can enhance the effectiveness of the airflow within the chassis. Table 2 on page 10 summarizes the effect of different numbers and configurations of box fans in the chassis. The purpose of the box fans is to improve circulation of air within the chassis. The box fans used in this experiment were chosen to fit the existing mountings in the chassis. The front fan is an 80-mm 35-CFM fan and the rear fan is a 60-mm 25-CFM fan. The goal of better circulation is to reduce the ambient temperature inside the chassis.
Layout and Airflow Considerations
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For the given chassis, different combinations of fans were tested. The tests were performed in an oven with a constant temperature of 35°C, and the internal ambient temperature of t h e ch a s s i s wa s m e a s u re d w i t h a t h e r m o c o u p l e . Th e thermocouple was located two inches from the processor as shown in Figure 8 on page 11. A control case was run with no added fans in the chassis and it resulted in an internal ambient of 48.2°C. The best improvement in ambient temperature was observed with the configuration of a single box fan added to the chassis as an intake fan in the rear wall of the system chassis. This fan placement resulted in a decrease in ambient temperature from 48.2°C to 43.6°C. See Table 2 for a complete summary of fan and chassis combinations. Also, note that the best case temperature (TCASE) for the processor was obtained w h e n t h e i n t e r n a l a m b i e n t t e m p e ra t u re wa s h e l d t o approximately 44.4°C. As shown in the test, the lowest ambient temperature is not always an indicator of the lowest T CASE . Ambient temperature is very dependent on the airflow path and how it is measured. The only way to completely verify a thermal solution is to measure TCASE. Table 2. Summary of Chassis Box Fan Configurations
Test #1 Off Off 68.8°C 48.2°C Test #2 Off Intake 69°C 48.7°C Test #3 Exhaust Intake 64.1°C 44.4°C Test #4 Intake Off 65.9°C 43.6°C
Thermal Test Condition Rear Wall System Fan Front Wall System Fan Processor, TCASE Internal Ambient Temperature
Layout and Airflow Considerations
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Rear Fan Power Supply
Front
Box Fan
Drive Bays
AMD-K6® Processor Regulator Heatsink
Inside Ambient Thermocouple
Box Fan Intake Vent
Figure 8. Standard Mid-Tower Case
Thermal Evaluation
Measuring Case Temperature
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Thermally Conductive Epoxy
Thermocouple
Figure 9. Measuring Case Temperature
Thermal Power Utility
A software utility has been developed to assist in testing thermal solutions. This utility executes a tight loop of instructions whose addressing and data have been defined to put the AMD-K6 processor in a state that dissipates the maximum thermal power. This utility can be used to determine if a given thermal solution is sufficient to maintain the specified TCASE limit. To use this utility, execute the DOS program, Maxpwr99.exe as follows: (Note: Do not execute the utility in a DOS window or with a memory manager loaded.)
Thermal Evaluation
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The Maxpwr99.exe utility is available under a nondisclosure a g re e m e n t . C o n t a c t yo u r l o c a l A M D s a l e s o f f i c e fo r information.
Recommended Thermal Solutions for the AMD-K6® Processor Family
AMD continually works with heatsink and fan manufacturers to identify thermal solutions for the AMD-K6 processor family. A list of solutions that maintain the case temperature of the AMD-K6 processor below the specified maximum temperature is available in the Recommended Thermal Solutions section of the AMD website, www.amd.com. Most of the solutions listed are available as-is and can be ordered as a combination or kit from the manufacturer. These solutions are available as a heatsink and fan combination. Other solutions require the use of a specific fan, mounted on top of the heatsink, capable of sufficient air flow (for example, 24 CFM for the 233-MHz AMD-K6 processor). In such cases, the fan and heatsink can be ordered separately from each manufacturer.
Additional Information
For more information about the following AMD-K6 processors:
AMD-K6 processor Models 6 and 7, see the AMD-K6® Processor Data Sheet, order# 20695 or contact your local AMD sales representative. AMD-K6-2 processor Model 8, see the AMD-K6®-2 Processor Data Sheet, order# 21850 or contact your local AMD sales representative. AMD-K6-III processor Model 9, see the AMD-K6®-III Processor Data Sheet, order# 21918 or contact your local AMD sales representative.
Additional Information
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Additional Information